For the collection and preparation of blood in blood-banks and hospitals, for the processing of medical fluids, for the processing of nutrient fluids to be administered to a patient and, in general, for the transfer of fluids to and from a donor, patient or recipient, increasing use is being made of blood bag, infusion-set and like systems in which plastic tubing is connected to a bag.
Frequently that plastic tubing must be sealed. While sealing can be effected with a clamp or some other valve arrangement, it has become a common practice to utilize thermal energy or high frequency energy to seal the tubing which is generally composed of a flexible plastic such as polyvinylchloride.
The sealing of medical tubing in this manner provides a hermetic and sterile seal to a bag system to which the tubing is attached and the seal is not fragile or susceptible to inadvertent opening.
Manually operated sealing devices for this purpose have been marketed, for example, by Sebra of Tuscon, the sealing device containing an electric circuit for the generation of high frequency energy, a coaxial cable transmitting this energy to the manually operated device which has a pair of sealing jaws formed with electrodes between which the tubing is insertable, and means for drawing the jaws together to clamp the tubing between the jaws, apply the high frequency energy to the electrodes to render the opposite internal surfaces of the tubing fusible, and causing these opposite surfaces to bond together to form the seal of the tubing.
The high frequency energy applied to the electrodes effects a dielective heating of the tubing between them since the electrodes function more or less as capacitor plates.
A system in which electrodes form capacitor plates to effect dielective heating between sealing jaws for squeezing the tubing between them is described in U.S. Pat. No. 4,013,860.
The device described in this patent contains a high frequency generator which produces electrical energy with a fundamental frequency of 40.68 MHz connected to the hand-held sealer unit by a 50 OHM coaxial cable. The tube sealer itself contains a resonant circuit which transforms the supplied energy to a high voltage at high frequency. This voltage, which can be about 1500 volts, is sufficient to generate enough heat in the polyvinylchloride to enable it to fuse between the sealing jaws.
The sealing process is begun by introducing the tubing between the two sealing jaws and placing these jaws together. The high frequency field is applied between these jaws which function as capacitor plates and the dielectric heating of the plastic tubing under the pressure of the jaws intense the tubing to bring the opposite inner surfaces of the tubing together and enables them to melt.
As the pressure and melting action causes the jaws to approach each other more closely, the dielectric heating effect increases because the field strength increases and results in greater indentation of the tubing, etc. The result is an "avalanche" effect which forms an effective seal relatively rapidly.
The duration of the process will depend upon the thickness of the tubing, the amount of high frequency energy supplied and the force which clamps the jaws together.
Normal sealing takes about 1 to 2 seconds and upon the elapse of a period sufficient to cause fusion of the opposite walls of the tubing, the supply of the high frequency current is terminated and the tubing can be held in its pinched state for an additional period of about 1 second of cooling to set the seal.
With earlier devices for this purpose, it was not always possible to apply the specific force necessary for an optimum seal. In other words, while it has been found that an optimum force of between 130 and 170 Newton is required and a residual force of up to 20 Newton is desirable to maintain the seal after the energy supply has been terminated, earlier devices for pinching the tube while applying high frequency energy have not always proved to be satisfactory.
Furthermore, the electrodes of earlier systems were transverse to the handle of the device and insertion of the tubing between the electrodes often could not be viewed adequately by the operator because the manner in which the device was held, partly obstructed view of the gap between the jaws.
By and large, therefore, the earlier devices for the sealing of medical tubing utilizes the foregoing principals could not be considered to be ergonomic.